as a judge I have a big dislike for when a student states they are going to do a form, then change that form. I will absolutely ding them on it.
The only issue that I take with this is in an open tournament. Coming from a hybridized system and having studied at schools that taught the purer versions of what I learned hybridized, I know first hand that my Saifa (for example) will not likely look like the judge's Saifa, because I was taught it under a different thought process. I may know the difference now, but as a blue belt, I never knew that there was another way.
Another example is the kata "Wankan"... to a shotokan person, it is a very differnet form than to a Shorin Ryu student.
Looking at the form based on technical merit (stances, technique, etc) is all one really has to go by in an open tournament. After that it's personal preference, and competitors aren't mind readers.
In a closed tournament however, you damned well better get the kata right if you say that you're gonna do it!